Use of N-(aminoalkyl) pyrrolidines as catalysts for the polyisocyanate polyaddition process

ABSTRACT

The present invention relates to a process for preparing polyisocyanate polyaddition products by reacting 
     (a) polyisocyanates with 
     (b) relatively high molecular weight compounds containing at least two isocyanate-reactive hydrogen atoms and 
     (c) chain-extending agents, in the presence of 
     (d) N-(aminoalkyl)pyrrolidine catalysts corresponding to formula (I)                    
     in which 
     R is a C 2-12  alkylene group (optionally containing O or N atoms but not isocyanate-reactive groups) and 
     R′ is hydrogen or a C 1-4  alkyl group, 
     (e) optionally, other known catalysts, and 
     (f) other known additives.

BACKGROUND OF THE INVENTION

This invention relates to the use of N-(aminoalkyl)pyrrolidines ascatalysts for the preparation of products by the polyisocyanate additionprocess. These catalysts may be used as a replacement for or incombination with known urethane catalysts, such as1,4-diazabicyclo[2.2.2]octane (DABCO), for the preparation of rigid orflexible polyurethane foams and other polyurethane products. In thecontext of the present invention, the term “polyurethane products” isintended to encompass all reaction products of polyisocyanates withcompounds containing at least two isocyanate-reactive hydrogen atoms.That is, the term “polyurethane” is understood to encompass, forexample, pure polyurethanes, polyurethane polyureas, or pure polyureas.

The rate of the reaction between isocyanate groups and compoundscontaining NCO-reactive hydrogen atoms is determined not only by thetemperature of the starting products and their structure butparticularly by the use of suitable catalysts. In practice, bases (forexample, tertiary amines such as triethylamine) are used mainly asnucleophilic catalysts, whereas organometallic compounds (for example,tin carboxylates such as tin(II) octoate) are used mainly aselectrophilic catalysts. The prior art processes are based on the jointuse of Lewis acids and Lewis bases, which is normally characterized bysynergistic effects. However, it is also known that amines areexclusively used as catalysts in a number of applications. However, onlya few of the large number of known amine catalysts (cf. Ullmann, 4thEdition, and Kunststoffhandbuch, Vol. VII, Polyurethane, Hanser-Verlag,Munich (1983)) have hitherto been adopted for use on a wide scale, with1,4-diazabicyclo[2.2.2]octane (DABCO), bis(2-dimethylaminoethyl) ether,triethylamine, dimethyl cyclohexylamine, dimethylethanolamine,dimethylbenzylamine, methylmorpholine, and ethylmorpholine being themost important. More particularly, of course, catalysts distinguished byhigh activity, economic production, and a broad range of applicationsare used. Another increasingly important consideration is thetoxicological evaluation of the catalysts with regard to processingsafety and odor emission. Many of the amine catalysts in use today, suchas DABCO or triethylamine, may be regarded as unsatisfactory in thisrespect because of their high volatility and the relatively intensiveamine odor that is carried over into the end product produced with suchcatalysts.

Amine catalysts containing an additional, isocyanate reactive groupcorresponding to the general formula

are described in German Offenlegungsschrift 2,116,535, which alsomentions, inter alia, compounds in which the two substituents R areattached to each other to form 3- to 6-membered rings. The use of onerepresentative member of this special class of compounds, namelyN-(2-aminoethyl)aziridine, is illustrated by Examples 10 and 16-18 ofthe German patent. In the Examples mentioned, this compound proved to bedistinctly poorer than the corresponding acyclic compounds with regardto the density, strength, and elasticity of the foams prepared (Example10) and particularly with regard to activity (Examples 16 to 18).

It has now surprisingly been found that certain pyrrolidine derivativesmay be used advantageously as catalysts for the preparation ofpolyurethanes. Compared with the above-mentionedN-(2-aminoethyl)aziridine and cyclic compounds other than those having5-membered rings, the compounds used in accordance with the inventionhave considerably greater activity that even surpasses that of theacyclic members disclosed in the above-cited German patentspecification. Another advantage is the faint odor and low volatility ofcompounds in which the isocyanate-reactive groups are bound in thepolymer, which leads to distinctly reduced odor emission in thepreparation of polyurethane products. In addition, other advantages havebeen observed, including, for example, ease of handling (because thepyrrolidines preferably used are liquid), good curing behavior, and, notleast, the very simple preparation of the compounds.

SUMMARY OF THE INVENTION

According to the present invention relates to a process for preparingpolyisocyanate polyaddition products comprising reacting

(a) polyisocyanates with

(b) relatively high molecular weight compounds containing at least twoisocyanate-reactive hydrogen atoms and

(c) chain-extending agents, in the presence of

(d) N-(aminoalkyl)pyrrolidine catalysts corresponding to formula (1)

in which

R is a C₂₋₁₂ alkylene group (optionally containing O or N atoms but notisocyanate-reactive groups) and

R′ is hydrogen or a C₁₋₄ alkyl group,

(e) optionally, other known catalysts, and

(f) other known additives.

DETAILED DESCRIPTION OF THE INVENTION

The polyisocyanate reaction products prepared according to the presentinvention are preferably cellular plastics.

The catalysts used according to the invention are known compounds. Thepreferred catalysts are prepared, for example, by addition ofpyrrolidine onto acrylonitrile, followed by reduction and, optionally,subsequent alkylation by known methods. The catalysts according to theinvention are colorless to pale yellowish compounds, the preferred typesbeing liquid, and are soluble in organic solvents and soluble ordispersible in water. The quantity of the catalysts is generally fromabout 0.01 to about 5% by weight, based on the isocyanate-reactivecompound. Although more than the above-mentioned quantity may be used,no advantage is gained.

Preferred compounds are catalysts corresponding to general formula (I)in which R is a 1,3-propylene group and R′ is hydrogen or C₁₋₄ alkyl.Suitable catalysts according to the invention include, for example,N-(2-aminoethyl)pyrrolidine, N-(2-(methylamino)ethyl)pyrrolidine,N-(3-aminopropyl)-pyrrolidine, N-(3-methylamino)propyl)pyrrolidine,N-(3-(ethylamino)propyl)pyrrolidine,N-(3-(propylamino)propyl)pyrrolidine, N-(4-aminobutyl)pyrrolidine,N-(3-amino-2-methylpropyl)-pyrrolidine, andN-(3-methylamino-2-methylpropyl)pyrrolidine. Preferred catalysts includeN-(3-aminopropyl)pyrrolidine, N-(3-methylamino)propyl)prrolidine,N-(3-(ethylamino)propyl)-pyrrolidine, andN-(3-(propylamino)propyl)pyrrolidine, with N-(3-aminopropyl)pyrrolidineand N-(3-(methylamino)propyl)-pyrrolidine being particularly preferred.

The isocyanate-reactive compounds which are used as component (b) in theprocess accordin9 to the invention are those used in previously knownprocesses for the preparation of polyurethanes and are described, forexample, in Kunststoffhandbuch, Vol. VII, Polyurethane, Hansen-Verlag,Munich (1963) or in Houben-Weyl, Makromolekulare Stoffe Vol. E 20. Theisocyanate reactive compounds have a molecular weight M_(n) of3000-10000, preferably 3000-6000, e.g. polyether-polyols such asBayfit®3973 or Bayfit®3963 (commercial product Bayer AG).

The compounds containing NCO groups used as component (a) in the processof the invention are the same compounds used in previously knownprocesses and are described, for example, in Kunststoffhandbuch, Vol.VII, Polyurethane, Hansen-Verlag, Munich (1983) or in Houben-Weyl,Makromolekulare Stoffe, Vol. E20.

When carrying out the process according to the invention, thesubstituted pyrrolidines are used in the same way as the previouslyknown catalysts. For example, the catalyst may be used in its liquidform or may be dissolved in a polyol or a suitable solvent. The catalystmay be used at any temperature - or under other conditions - eitheralone or in combination with other known catalysts that are suitable forthe preparation of polyurethanes. Suitable other catalysts includeorganic or inorganic tin compounds or other organometallic compounds;tertiary amines, alkanolamines, cyclic amines, polyamines, and the like;alkali metal compounds; and other co-catalysts.

The catalysts according to the invention are preferably used in aquantity of at least 50% by weight, based on the total quantity ofcatalyst used.

The process according to the invention is suitable for conventionalproduction methods, including, for example, one-shot or prepolymerprocesses for the preparation of polyurethane foams, polyurethaneelastomers, polyurethane coatings, and the like, and for thecrosslinking reaction which is often desirable after the directpolyaddition.

All other conditions are the same as those used in conventional urethanepolyaddition processes. In each case, other known additives may be used,including chain-extending agents, blowing agents, foam stabilizers,emulsifiers, dyes, pigments, and fillers.

The above-mentioned catalysts of the invention accelerate thepolyaddition reaction to a considerable extent so that the quantity ofcatalyst required is very small. Because the catalyst compoundsaccording to the invention have only a faint odor and because theyrepresent substantially nonvolatile liquids and incorporable compounds,the polyurethane products obtained are free from unwanted odors.

The following examples further illustrate details for the process ofthis invention. The invention, which is set forth in the foregoingdisclosure, is not to be limited either in spirit or scope by theseexamples. Those skilled in the art will readily understand that knownvariations of the conditions of the following procedures can be used.Unless otherwise noted, all temperatures are degrees Celsius and allparts and percentages are parts by weight and percentages by weight,respectively.

EXAMPLES Examples 1 to 6

These Examples demonstrate the high catalytic activity ofN-(3-aminopropyl)pyrrolidine and N-(3-methylamino)propyl)pyrrolidine incomparison with analogous catalysts which do not contain a pyrrolidinering in a polyurethane cold-cure flexible foam system.

The following catalysts were used:

Catalyst 1: N-(3-aminopropyl)piperidine

Catalyst 2: N-(3-aminopropyl)-N′-methylpiperazine

Catalyst 3: 3-dimethylaminopropylamine

Catalyst 4: N-(3-aminopropyl)pyrrolidine

Catalyst 5: N-(3-(methylamino)propyl)pyrrolidine

The catalysts have the following formulas:

Catalysts 4 and 5 correspond to the invention, with the other catalystsbeing comparison catalysts.

Component A:  37.10 parts mixture of 80% 2,4-toluene diisocyanate and2,6-toluene diisocyanate (in a ratio of 80:20) and 20%4,4′-diisocyanatodiphenylmethane with polymeric components (NCO content44.5 ± 0.5% by weight) (Desmodur ® VT 06, a commercial product of BayerAG) Component B: 100.00 parts polyether polyol (OH value 28 ± 2 mgKOH/g) prepared by reaction of trimethylolpropane (TMP) with propyleneoxide (PO) and sub- sequent reaction with ethylene oxide (EO) in a PO:EOratio of 82:18  3.00 parts water  0.05 part 70% solution ofbis(2-dimethylaminoethyl) ether in dipropylene glycol (DPG)  0.25 part33% solution of diazabicyclo[2.2.2]octane (DABCO) in DPG  0.20 part foamstabilizer B4617 (Goldschmidt AG)  0.80 part polyether polysiloxane asstabilizer (Stabilisator IS 50, a product of Bayer AG)   0.6 partcatalyst 1 to 5

Component A is combined with component B and the mixture is thoroughlymixed for 6 seconds using a high-speed stirrer. The reaction mixture isthen foamed in an open mold at room temperature.

The results obtained with the various catalysts are set out in Table 1.

TABLE I Cream time Gel time Rise time Example Catalyst (sec) (sec) (sec)1 None 9 108 213 2 1 9 105 210 3 2 8  75 150 4 3 7  52 115  5* 4 6-7  48100  6* 5 4-5  46  93 *Examples according to the invention

Foams having a satisfactory foam structure were obtained.

What is claimed is:
 1. A process for preparing a polyisocyanatepolyaddition product comprising reacting (a) a polyisocyanate with (b) arelatively high molecular weight compound containing at least twoisocyanate-reactive hydrogen atoms and (c) a chain-extending agent, inthe presence of (d) an N-(aminoalkyl)pyrrolidine catalyst correspondingto the formula

in which R is a C₂₋₁₂ alkylene group (optionally containing O or N atomsbut not isocyanate-reactive groups) and R′ is hydrogen or a C₁₋₄ alkylgroup, (e) optionally, other known catalysts, and (f) other knownadditives.
 2. A process according to claim 1 wherein R is a1,3-propylene group and R′ is hydrogen or C₁₋₄ alkyl group.
 3. A processaccording to claim 1 wherein the N-(aminoalkyl)pyrrolidine catalyst isN-(3-aminopropyl)pyrrolidine and N-(3-(methylamino)propyl)pyrrolidine.4. A process according to claim 1 wherein the polyisocyanatepolyaddition product is a cellular plastic.